Socket protector, from Yamamoto 9-Pin socket

All tube sockets will give a good contact condition for a limited time only. At first, you get contact resistance, which lowers mainly the filament voltage. This can easily be 0.1 Volts per pin. So this can lead to a 6Volts tube being heated with 5.8 Volts. When the contact quality gets worce, you will get scratch noise when you touch the tube. This is the beginning of microphonic effects durung normal use. Microphonic effects can make chassis hum from the transformer audible, and acoustic coupling via the loudspeakers. (ringing effect). The ultimate damage comes when you have a loose control grid contact (g1). This will make the tube draw the highest possible current it can do, and burn down the tube. You will blame the tube for it! So you replace the tube and it works normal. After some weeks or months it happens again, and you will now blame anything, but still not the socket.

So when a socket developes scratch noise, what you can do is following:

1. Don't use any kind of silver or other metal containing metallic "contact paint" or junk like this. This may help, but may give dangerous damage to your amplifier.
2. Use a good contact oil for high impedance contacts. (We sell this)
3. Better is to REPLACE the socket with a new one.
4. If a replacement is difficult to so, use a so called socket protector. This is a special socket you plug into the old socket

A socket protector is usefull when you basically would like to replace the old socket, but for mechanical reasons you can not do it. The standard yamamoto 9-pin socket, the PCB mounting type, can be easily modified to become a socket protector!

Here is how that is done:

	First, you remove the pins with a normal screwdriver. The center pin, you see romoved in this picture, but actually you can also leave it in, and just cut it off.
	Here is a detailed picture. Look at the left side of the pin, there is a pip here, which is used to make sire wires won't come off. Because of this pip, you can not plug thhis into a normal tube socket. However the diameter of the rest if the pin is the same a any 9-pin tube! So all we need to do, is change the shape of this pip, and the socket protector is ready.
	Here is how it's done. A normal kitchen grinding stone is used here, but a small file, or abrasive paper can be used also. You grind a V-shape at the tip, and the outside diameter of the "V" is 1.3mm. The outside diameter is not very critical, but you must keep it larger than the rest of the pin. Click on the left picture, it is self explaining. The metarial is so called "spring" bronze, and is very pleasant to work on.
	Here you see the self made socket protector used in the Russian L3-3 tester. This tester obviously was used by the previous owner (Czech Meteorologic Institute in Brno) for 9-pin sockets only. The contact quality was reduced. Perhaps they disposed of the tester for that reason, thinking it was bad. You can also use the socket protector with amplifiers, the same way.